The present invention relates to an intelligent control circuit used to control the power supplied to an electrode of the type used in the electrical arc welding process. The control circuit protects welders against electric shocks by blocking the voltage potential from electrode or work-piece, depending on the polarity setting of the welder.
The vast majority of accidents that involve electrical shock, during the arc welding process, occur when the user changes rods. The conditions for receiving electrical shock are greatly enhanced when dealing with wet or humid environments. The differences in individual body resistance is also a factor. These conditions can be even more hazardous when the environment is a wet mineralized process such as found in potash refining.
When the user changes rods he is subjected to the full welder output voltage potential. If the resistance path through the user is low enough to conduct current, then electrical shock occurs. The shocks can range from mild to severe, even to the point of fatality. The locations that workers must weld in do not lend themselves well to former methods of protection, such as rubber mats, rubber gloves, anti-moisture sprays, etc.
It is well known that a serious hazard exists in the open circuit voltage that users are subjected to when changing electrodes. The degree of risk is intensified by damp or wet environmental conditions. In previous inventions there were various types of manual or automatically operated circuits incorporating mechanical contactors, the main function of which was to disconnect the electrode from the power supply when welding was ceased. However, those mechanical contactors suffer a major drawback, in that they have a low time of response. None of the suggested electro/mechanical circuits were able to offer a reliable and efficient operation to gain acceptance amongst welders. In another previous invention that utilized a solid state design also had design flaws that rendered the design unreliable and unsafe for use in all but the least hazardous environments.
In U.S. Pat. No. 4,514,615 is shown an arrangement of this type which uses an SCR Thyristor switch to control the current to the electrode in dependence upon a control circuit which detects the impedance of the electrode and only allows flow of current in the event that the impedance is less than 400 ohms.
It is one object of the present invention to provide a control apparatus for the electric welder which is more practical in its operation thus providing an apparatus which is useable in the industry.
According to a first aspect of the invention there is provided a control apparatus for controlling supply of voltage from the supply unit to the electrode of a DC electric welder for protecting a user of the electrode against electric shock when changing rods in the electrode, the apparatus comprising:
an input terminal for connection to a the supply unit for receiving therefrom a DC current for supply to the electrode;
an output terminal for connection to the electrode for supplying the current from the supply unit to the electrode for powering the electrode during use;
a supply line connected between the input terminal and the output terminal;
an electronic current switch in the supply line operable to transmit or to not transmit the current from the input terminal to the output terminal;
a detector circuit arranged to detect the electrical resistance between the output terminal and ground;
and a control circuit arranged to actuate the switch to effect transmission of current only if the resistance detected is less than or equal to 120 ohms.
Preferably the control circuit is arranged to actuate the switch to effect transmission of current only if the resistance detected is less than or equal to 40 ohms
Preferably the switch is an SCR thyristor having a gate which is triggered by the control circuit.
Preferably the control circuit is arranged such that the gate of the thyristor is triggered only for a period of time and the gate is then not triggered during normal welding.
Preferably the control circuit is arranged such that the gate is triggered for a period just long enough to complete an arc between the electrode and a workpiece.
Preferably the control circuit is arranged such that the period is of the order of three seconds.
Preferably the control circuit is arranged such that there is a delay before the switch is triggered.
Preferably the control circuit is arranged such that the delay is of the order of 0.5 seconds.
Preferably the control circuit includes a programmable micro-controller chip which allows the chip to be programmed to specific parameters.
Preferably the control circuit includes a programmable micro-controller chip which allows the chip to automatically test all critical components in the control circuit and relate any fault information to the user.
Preferably there are provided reverse polarity protection diodes on all connections from the control circuit to the supply line.
According to a second aspect of the invention there is provided a control apparatus for controlling supply of voltage from the supply unit to the electrode of a DC electric welder for protecting a user of the electrode against electric shock when changing rods in the electrode, the apparatus comprising:
an input terminal for connection to a the supply unit for receiving therefrom a DC current for supply to the electrode;
an output terminal for connection to the electrode for supplying the current from the supply unit to the electrode for powering the electrode during use;
a supply line connected between the input terminal and the output terminal;
an SCR thyristor switch in the supply line operable to transmit or to not transmit the current from the input terminal to the output terminal;
a detector circuit arranged to detect the electrical resistance between the output terminal and ground;
and a control circuit arranged to actuate the SCR thyristor switch to effect transmission of current only if the resistance detected is less than a predetermined value;
wherein the control circuit is arranged such that the gate of the thyristor is triggered only for a period of time and the gate is then not triggered during normal welding.
According to a third aspect of the invention there is provided a control apparatus for controlling supply of voltage from the supply unit to the electrode of a DC electric welder for protecting a user of the electrode against electric shock when changing rods in the electrode, the apparatus comprising:
an input terminal for connection to a the supply unit for receiving therefrom a DC current for supply to the electrode;
an output terminal for connection to the electrode for supplying the current from the supply unit to the electrode for powering the electrode during use;
a supply line connected between the input terminal and the output terminal;
an electronic current switch in the supply line operable to transmit or to not transmit the current from the input terminal to the output terminal;
a detector circuit arranged to detect the electrical resistance between the output terminal and ground;
and a control circuit arranged to actuate the switch to effect transmission of current only if the resistance is less than a predetermined value;
wherein the control circuit includes a programmable micro-controller chip which allows the chip to be programmed to specific parameters.
The distinct feature of the present invention is a control circuit comprised of electronic components, which are reliable, efficient, and extremely fast operation. The control circuit has several design advantages over previous designs that enable the unit to work in even the harshest environments. The unit contains a micro-controller that is used for control of the device and can also test all critical onboard active electronic components. The unit can be used in both reverse polarity configurations as well as straight polarity configurations. The power control circuit prevents electrical power from reaching the electrode until required and the device does not at all interfere with the welding process.
According to the above features, from a broad aspect, there is provided a micro-controller based control circuit for controlling the power supplied to the electrode. The control circuit comprises voltage level detection circuitry used to detect the resistance between the electrode and the work-piece. The control circuit utilizes proprietary embedded firmware to control the unit and to internally test all functions. A power control device is used in series with the electrode in reverse polarity or in series with the work-piece in straight polarity. The power feeding device is controlled by the resistance detection device so as to render the power feeding device conductive when the dynamic voltage drop within the control circuit falls to a predetermined threshold. This threshold is maintained internally within the control circuit and is fixed at 40 ohms or less. Extensive testing has revealed that at resistance values larger than 40 ohms, a wet human body can be subjected to electrical shock by contacting the electrode and the work-piece simultaneously. This is especially true when air arcing is used and the open circuit voltage is very high.